The present invention relates to a method of pretreating crosslinkable polymers and co-polymers with organo-metallic compounds, inorganic metallic salts or lanthanides prior to crosslinking by free radical initiators using ultra-high frequency radiation (UHF) or hot air heating systems to form crosslinked polymers with non-tacky surfaces.
Prior to the present invention, crosslinked polymers and co-polymers using organic peroxide initiators have been produced in a molten bath known as liquid curing medium (LCM), in a steam pipe, or in other closed systems. For thick and complicated profiles, the UHF beams combined with hot air heating has been used for crosslinking the polymers. The descriptions in technical literature indicate that crosslinking is being carried out by sulfur employing the UHF hot air curing method and that crosslinking with organic peroxides results in incomplete crosslinked and tacky surfaces of the articles. (e.g., see Farkenfabriken Bayer, specification dated Mar. 2, 1962, Levapren 450 (ethylene-vinylacetate), paragraph 7.1.1 to 7.1.5 as well as specification dated Dec. 1, 1965, Urepan (urethane rubber), page 15, paragraph 1 and Chemische Werke Huls May, 1976, 3rd edition, Buna AP (EPM/EPDM) operational procedure "processing description," page 4.) Tackiness is more pronounced with highly filled and oil extended co-polymers like ethylene-propylene co-polymer (EPM), ethylene-propylene-dienemonomer co-polymer (EPDM), styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), natural rubber (Cis-1,4-polyisoprene) (NR), isoprene rubber (IR), ethylene-vinylacetate co-polymer (EVA), acrylnitrile-butadiene-styrene co-polymer (ABS), styrene-butadiene-styrene rubber (SBS), styrene-isoprene-styrene co-polymer (SIS), chloroprene rubber (CR), chlorinated polyethylene (CM) and polymethylene rubber. The present invention overcomes the problem of the tackiness of the surfaces of crosslinked polymers by the treatment of the crosslinkable polymers, copolymers or the shaped articles thereof prior to the crosslinking of such polymers with the free radical initiators even in the presence of oxygen.